In such machines, molten material is fed from the screw barrel of an extruder via a manifold sprue bushing in an inlet melt channel of a hot runner system and there in a plurality of output melt channels fluidically connected to and downstream from the inlet melt channel.
Such an injection molding apparatus is known from the brochure “manner micro-män 50” of Otto Männer GmbH, which is made available on the company website http://www.maenner-group.com and whose content is herein incorporated by reference.
Known injection molding machines have a first machine platen, fixed to the machine base and a second machine platen which is movable with respect to the first machine platen. The first machine platen has an opening for the machine nozzle of the machine injection unit. A mold plate is mounted on the surface of the first machine platen opposite to the second machine platen. A hot runner manifold with hot runner nozzles is mounted on the surface of the mold plate. Moving means for the actuators of the hot runner nozzles are often mounted on the mold plate or on the machine platen.
This construction shows a large area of contact between the machine platen and the mold plate and between the mold plate and the hot runner manifold which assists heat conduction between these components resulting in energy loss in the hot runner system and thermal expansion of the machine platen. Further, the actuation means of valve pins are located behind the hot runner nozzles which results in a lower precision in parallel actuation of the nozzles resulting from positioning of the actuators laterally next to the mold plate and hot runner system. A positioning of the actuation means behind the nozzles also results in the need of a long distance manifold sprue bushing and inlet melt channel respectively.
It is therefore the object of the present invention to provide an injection molding apparatus improving the specified drawbacks for producing high quality small and miniature plastic parts.
An injection molding apparatus improving at least some of the specified drawbacks is described in the German patent application DE 10 2011 116 053. The content of this application is also incorporated herein by reference.
The invention relates to an injection molding machine for producing injection-molded parts having an injection station comprising an injection nozzle arranged on a machine platen for discharging melt, wherein a molding tool is arranged on the machine platen which defines a cavity corresponding to the injection-molded part, wherein the molding tool comprises at least one first tool element which is stationary relative to the machine platen and one second tool element which is displaceable relative to the first tool element between an open and a closed position by means of a closing device, and wherein the injection nozzle is connected to at least one inlet of the cavity arranged on the first tool element by means of a hot runner system.
This type of injection molding machine is known from DE 10 2005 015 242 A1. It comprises a molding tool having two tool elements which define a cavity adjoining both tool elements for producing an injection-molded part. A first tool element is fixed on a first machine platen arranged stationary to the injection nozzle and a second tool element is fixed on a second machine platen which is movable to open and close the molding tool on the first machine platen toward and away from same. The first tool element has an indentation on its rear side facing the injection nozzle in which a hot runner system is arranged which connects the injection nozzle to the inlets provided on the cavity for the melt. The hot runner system is thermally insulated from the first tool element and the machine platen. The hot runner system has the advantage that the melt within the hot runner system remains capable of flowing when the injection-molded part solidifies such that virtually no residual sprue remains on the injection-molded parts after they're removed from the molding tool. This enables omitting the production step of separating the sprue from the injection-molded part. The hot runner system moreover has the advantage of reducing the plastic material used during the injection molding because the melt remaining in the hot runner system can be used for injection molding at least one further injection-molded part. Yet the injection molding machine does have the disadvantage of being of relatively large dimensions. Further disadvan-tageous is that the first, so-called hot molding tool is still relatively complex and expensive.